Visitors to Melbourne for the Boxing Day Test might not have experienced much heat on or off the field during the one-sided contest between Australia and the West Indies, which was played in temperatures that barely climbed into the 20s.

But if they hang around for a few days, Melbourne will warm back into the mid- to high-30s by Thursday, making it likely the city will experience at least its third-warmest December on record, Ben McBurney, a meteorologist at Weatherzone, said.

So far this month, Melbourne's average maximums are running at 27.4 degrees, a full degree warmer than Sydney well to the north.

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The blaze in the Victorian town of Wye River on Christmas Day.Credit:Keith Pakenham / CFA

Dominant highs in the Tasman Sea have kept the Harbour City stuck in a moderate spell with daily tops in the mid-20s that has at least another week to run, Mr McBurney said.

Such mild conditions would probably be welcomed in Adelaide as residents there head for "comfortably" that city's hottest December on record, he said.

Temperatures in the SA capital will lurch back towards the high 30s by Wednesday, with the hot conditions spilling back into Victoria and elevating the fire risks around the popular holiday strip around Lorne.

A year of extremes

The gradual background warming of the planet caused primarily by the build-up in greenhouse gases is being amplified this year by one of the strongest El Nino events on record.

During El Nino years, the Pacific Ocean's easterly winds stall or reverse, resulting in less heat being absorbed and altering rainfall patterns that can have worldwide impacts.

Floodwater rises as the River Calder bursts its banks, flooding the English town of Mytholmroyd.Credit:Getty Images

A classic outcome is South America cops heavier than usual rain, a result evident this past week with about 140,000 people forced to evacuate their homes in a region taking in parts of Argentina, Brazil, Paraguay and Uruguay.

Floods Minister Rory Stewart said rainfall levels in the flood-hit areas were unprecedented, while others have described them as as being of biblical proportions.

"We're looking potentially again today at maybe a month's rainfall coming in a day. That's falling on ground that's very saturated. As the rain falls, the rivers respond very quickly," he told BBC Radio 4.

Northern Australia floods

While much of Australia has been crying out for rain, parts of the north are being flooded as a deep low pressure system moves eastwards.

A woman died after her car got caught in a floodway in the Northern Territory, becoming the second likely death from flooding since Christmas.

A police helicopter spotted the vehicle in floodwaters about four kilometres from the remote Beswick community, east of Katherine, on Sunday night. It's believed the elderly woman was one of five people in the car.

Hopes are fading in the search for a 28-year-old man missing from Peppimenarti in the Daly River region since Christmas Day.

The Flinders Highway near Julia Creek was cut due to flood waters on Sunday morning which also made it difficult for emergency teams to reach a derailed Aurizon train 150m from the highway at Quarrells.

The freight train spilled diesel fuel and 200,000 litres of sulfuric acid while three Aurizon employees suffered minor injuries in the incident in which all 26 carriages and the locomotive came off the tracks.

The tropical low is expected to continue to drift eastwards and the bureau is warning about the potential for flash flooding north of Townsville, especially around Innisfail, on Tuesday.

The bureau is also predicting heavy falls of as much as 400mm in parts of northern Queensland over the coming eight days:

Weatherzone's Mr McBurney said the course that low pressure system tracks will have a big influence on weather conditions for Sydney and other parts of south-eastern Australia over the coming days.

According to one model, the low will shift southwards, bringing cloud and rain.

"If that low comes down it could really break up the heat," he said, potentially easing fire weather conditions until the middle of January.